Re: Looking for help to understand external filter driver code

From: Lars Schneider <larsxschneider@gmail.com>
Date: Jul 19, 2016, 20:44 UTC
Message-ID: <7B44C694-7CB2-411D-9CC6-7334CCBAD20B@gmail.com>
In-Reply-To: <xmqqlh0xfoho.fsf@gitster.mtv.corp.google.com>

On 19 Jul 2016, at 20:53, Junio C Hamano <gitster@pobox.com> wrote:

Show 14 quoted lines

> Junio C Hamano <gitster@pobox.com> writes:
> 
>> The key benefit of this arrangement is the above can be done without
>> having to do poll() to flip between reading and writing that is
>> needed to avoid deadlocking, which kept the code simpler.  A later
>> conversion of the write side into async does not fundamentally
>> change anything from the original arrangement.
> 
> Translation: I was too lazy to worry about doing poll()/select()
> when I did it originally.  As long as you can do so correctly, be my
> guest to reduce one process by having the main process do both
> reading and writing.
> 
> ;-)

Thanks a lot for this explanation. My goal is to add an option to the clean/smudge filter config that instructs Git to keep the external filter process running. Whenever Git encounters a file to be filtered then it would continue to talk to the filter process over a simple pipe protocol:

Git writes --> 4 byte filename length Git writes --> filename string Git writes --> 4 byte content length Git writes --> content string Git reads <-- 4 byte filtered content length Git reads <-- filtered content

I still need to read more about poll()/select() but it looks to me as if these functions are only required if Git doesn't know what to expect. With the sketched protocol above that wouldn't be the case. Therefore, I wonder if I would need to use poll()/select()?

Thanks, Lars